Micro-electro-mechanical system device with enhanced structural strength

ABSTRACT

The invention provides a MEMS device with enhanced structural strength. The MEMS device includes a plurality of metal layers, including a top metal layer with a plurality of metal segments. The metal segments are individually connected to an adjacent metal layer immediately under the top metal layer through at least one supporting pillar, and there is no dielectric layer between the metal segments and the adjacent metal layer immediately under the top metal layer. The metal layers except the top metal layer are respectively connected to their adjacent metal layers through at least one supporting pillar and a dielectric layer filling in between.

CROSS REFERENCE

The present invention claims priority to TW 102136681, filed on Oct. 11,2013.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a micro-electro-mechanical system(MEMS) device with enhanced structural strength, especially a MEMSdevice having a top metal layer with a plurality of metal segmentsand/or a lowest metal layer including a continuous structure.

2. Description of Related Art

FIG. 1 shows a prior art MEMS device 10, which for example can be usedfor a stator or a rotor. The MEMS device 10 includes amicro-electro-mechanical structure 101 and a signal transmissionstructure 102, wherein an operation of the MEMS structure 101 generatesan electric signal and the electric signal is transmitted through thesignal transmission structure 102. When the MEMS device 10 is a stator,the MEMS structure 101 for example can be connected to a substrate Subthrough a fixing member 103. When the MEMS device 10 is a rotor, theMEMS structure 101 for example can be connected to the substrate Subthrough a flexible member (shown schematically as a spring for example).The MEMS device 10 can be manufactured by a CMOS semiconductormanufacturing process, in which plural metal layers M1-Mt and pluraldielectric layers are deposited and patterned on the substrate Sub, andplural via plugs are formed in the dielectric layers to connect themetal layers so as to form a designed structure.

The prior art MEMS device 10 has the following structure features:

1. The top metal layer Mt has a continuous structure.

2. The signal transmission structure 102 is formed by a portion M1S ofthe first metal layer M1; therefore, in order to prevent the signaltransmitted through the signal transmission structure 102 from beingaffected by a nearby electric field and also avoid stiction which mayoccur in the manufacturing process and in the operation of the MEMSdevice, the second metal layer M2 has a disconnection area above theportion M1S to leave a buffer space. However, this recess weakens thestrength of the MEMS structure 101.

When the strength of the MEMS structure 101 is not enough, it is liableto warp or distort. For example, when the environment temperatureincreases, the MEMS device 10 can easily deform to affect theperformance of the MEMS device 10.

FIG. 6A shows deformation of the MEMS device 10 as the temperatureincreases. In the figure, the horizontal axis represents distance in thedirection X of FIG. 1, and the vertical axis represents deformation,wherein the temperature T2 is higher than the temperature T1. As shownin the figure, the deformation at temperature T2 is higher than thedeformation at temperature T1, and the deformation increases alone thedirection X to an extent that can affect the stability of the structureand the function of the device in operation.

In view of the aforementioned deficiencies of the prior art, the presentinvention provides a MEMS device with enhanced structure strengthwhereby there is little or no deformation caused by temperature changeor other reasons, to avoid stiction, maintain the structure stability,and improve the signal transmission performance.

SUMMARY OF THE INVENTION

In one perspective, the present invention discloses a MEMS device withenhanced structural strength, which includes: a MEMS structure,including a plurality of metal layers which include a top metal layer,the top metal layer including a plurality of metal segments which arenot directly connected with one another; and a signal transmissionstructure under the MEMS structure for transmitting an electric signalgenerated by the MEMS structure; wherein each of the metal segments isindividually connected to an adjacent metal layer through at least onesupporting pillar, and there is no dielectric layer between the metalsegments and the adjacent metal layer, and wherein except the top metallayer, the other metal layers are respectively connected to theiradjacent metal layers through at least one supporting pillar, with adielectric layer at least partially filling between two adjacent metallayers.

In one embodiment of the present invention, the MEMS device withenhanced structural strength further includes a fixing member or aflexible member connected to the MEMS structure.

In one embodiment of the present invention, the fixing member isconnected to a lateral side of the MEMS structure.

In another embodiment of the present invention, the MEMS device furtherincludes a recess under the MEMS structure at a location above thesignal transmission structure.

In one embodiment, a lowest metal layer of the MEMS structure iscontinuous to the fixing member at the lateral side of the MEMSstructure and does not have a disconnection area above the signaltransmission structure.

In the aforementioned embodiment, preferably, the signal transmissionstructure does not comprise a metal layer as defined by CMOSmanufacturing process terminology, and the signal transmission structureincludes a conductive wiring at a level below the metal layer.

In one embodiment, the fixing member is connected to a bottom of theMEMS structure.

In the aforementioned embodiment, preferably, the MEMS device furtherincludes a recess under the MEMS structure at a location above thesignal transmission structure, wherein the recess is farther from thecenter of the MEMS structure than the fixing member is.

In another perspective, the present invention discloses a MEMS devicewith enhanced structural strength, which includes: a MEMS structure,including a plurality of metal layers; a fixing member, which isconnected to a lateral side of the MEMS structure; and a signaltransmission structure under the MEMS structure, for transmitting anelectric signal generated by the MEMS structure; wherein a lowest metallayer of the MEMS structure is continuous to the fixing member at thelateral side of the MEMS structure and does not have a disconnectionarea above the signal transmission structure, and wherein the signaltransmission structure does not comprise a metal layer as defined byCMOS manufacturing process terminology and the signal transmissionstructure includes a conductive wiring at a level below the metal layer.

In another perspective, the present invention also discloses a MEMSdevice with enhanced structural strength, which includes: a MEMSstructure, including a plurality of metal layers; a fixing member, whichis connected to a bottom of the MEMS structure; and a signaltransmission structure under the MEMS structure for transmitting anelectric signal generated by the MEMS structure; wherein the MEMSstructure further includes a recess under the MEMS structure at alocation above the signal transmission structure, and the recess isfarther from the center of the MEMS structure than the fixing member is.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below, with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art MEMS device.

FIG. 2 shows a MEMS device with enhanced structural strength accordingto an embodiment of the present invention.

FIG. 3 shows a MEMS device with enhanced structural strength accordingto another embodiment of the present invention.

FIG. 4 shows a MEMS device with enhanced structural strength accordingto yet another embodiment of the present invention.

FIG. 5 shows a MEMS device with enhanced structural strength accordingto yet another embodiment of the present invention.

FIGS. 6A-6E show deformation amounts of the MEMS devices of FIGS. 1-5,respectively.

FIG. 7 shows a MEMS device with enhanced structural strength accordingto yet another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings as referred to throughout the description of the presentinvention are for illustrative purpose only, to show the interrelationsbetween the regions, layers and components, but not drawn according toactual scale. The orientation wordings in the description such as:above, under, left, or right are for reference with respect to thedrawings, but not for limiting the actual product made according to thepresent invention.

FIG. 2 shows a MEMS device 20 with enhanced structural strengthaccording to an embodiment of the present invention. The MEMS devicewith enhanced structural strength 20 includes a MEMS structure 201 and asignal transmission structure 202 under the MEMS structure 201, whereinthe MEMS structure 201 generates an electric signal according to arelative movement with respect to other parts (not shown) of the deviceand the electric signal is transmitted through the signal transmissionstructure 202. The MEMS structure 201 includes plural metal layersM2-Mt; that is, from the second metal layer M2 to the top metal layerMt. (By customary terminology in the CMOS semiconductor manufacturingprocess, after transistor devices and contacts to the gate, source anddrain of the transistor device are formed, the next deposited metallayer is referred to as the first metal layer, and the second metallayer is the next metal layer to the first metal layer. Although thecontacts to the gate, source and drain of the transistor device are madeof metal, they are referred to as the “contact layer”, not “metallayer”.) The top metal layer Mt includes plural metal segments Mt1 whichare not directly connected with one another; instead, each of the metalsegments Mt1 is individually connected to an adjacent metal layer Mt−1(“adjacent metal layer” means a metal layer that is immediately above orunder; the metal layer Mt−1 is immediately under the top metal layer Mt)through at least one supporting pillar. In this embodiment, besides theat least one supporting pillar which connects a corresponding metalsegment Mt1 to the adjacent metal layer Mt−1, there is no dielectriclayer between the metal segments Mt1 and the adjacent metal layer Mt−1.The other metal layers (for example, from the second metal layer M2 tothe metal layer Mt−1) are respectively connected to their adjacent metallayers through at least one supporting pillar, and there can be adielectric layer at least partially filling (shown as fully filling inthe figure) between two adjacent metal layers. The MEMS device 20 has anenhanced structure strength by the above structure; in particular, thedeformation caused by a temperature increase can be reduced.

FIG. 6B shows deformation of the MEMS device 20 as the temperatureincreases. Compared with FIG. 6A, the deformation of the MEMS device 20as shown in FIG. 6B is greatly reduced. Due to the reduced thermaldeformation, the stiction is better avoided, and the structure stabilityand signal transmission performance of the device are also improved.

In one embodiment, the MEMS device 20 of FIG. 2 can be used for a statoror a rotor. When the MEMS device 20 is a stator, the MEMS structure 201can be connected to a substrate Sub through a fixing member 203. Whenthe MEMS device 20 is a rotor, the MEMS structure 201 can be connectedto another part of the MEMS device 20 through a flexible member (shownschematically as a spring for example). The fixing member 203 forexample can be formed by the metal layers M1-Mt and the dielectriclayers. Note that what is shown in the figure is only one example. Thefixing member 203 can have any shape and any height; for example, thefixing member 203 can be formed without the top metal layer Mt and thedielectric layer under it. In this embodiment, there is a recess 22under the MEMS structure 201 at the location above the signaltransmission structure 202, for forming a buffer space. That is, thelowest metal layer (M2 in this embodiment) of the MEMS structure 201 hasa disconnection area above the lowest metal layer signal transmissionstructure 202. The dielectric layer above the lowest metal layer canalso be partially removed (as shown by this embodiment), or thedielectric layer above the lowest metal layer can completely remain. Thesignal transmission structure 202 is formed by a portion M1S of thefirst metal layer M1.

FIG. 3 shows a MEMS device 30 with enhanced structural strengthaccording to another embodiment of present invention. The majordifference between the MEMS devices 20 and 30 is that the MEMS device 30does not have the recess 22 of the MEMS device 20, and the signaltransmission structure 302 of the MEMS device 30 is formed by conductivewirings S at a contact layer V without the first metal layer M1. Becausethe signal transmission structure 302 does not include the first metallayer (and any higher metal layer) and is composed of the conductivewirings S at a level below the first metal layer, leaving more room forthe buffer space, the lowest metal layer (M2 in this embodiment) doesnot need to have a disconnection area above the signal transmissionstructure 302 at a location nearby the fixing member 301, and thereforethe structure strength is enhanced. By customary terminology in the CMOSsemiconductor manufacturing process, “contact layer” refers to aconnection layer between the substrate Sub and the first metal layer M1,and the connection layers above the first metal layer M1 are usuallyreferred to as “via layers”. This embodiment removes the recess, whichimproves the structure strength of the MEMS device 30 to thereby reducethe thermal deformation. The material of the conductive wirings S forexample can be metals such as tungsten, titanium, or their metalcompounds. The conductive material wirings S can extend horizontallyalong any direction on the substrate Sub and are not limited to a columnshape.

Similar to the embodiment of FIG. 2, the MEMS device 30 can be used fora stator or a rotor. When the MEMS device 30 is used for a stator, theMEMS structure 301 can be connected to the substrate Sub through afixing member 303. When the MEMS device 30 is used for a rotor, the MEMSstructure 301 can be connected to another part of the MEMS device 300through a flexible member (shown schematically as a spring for example).That “the recess is removed” can be regarded as a direct and completeconnection between the lowest metal layer M2 of the MEMS structure 301and the fixing member 303 (or the flexible member). Note that theembodiments of FIGS. 2 and 3 show that the lowest metal layer of theMEMS structure 301 is the second metal layer M2, which is only anillustrative example but not for limiting the application of the presentinvention. The lowest metal layer of the MEMS structure can be a highermetal layer such as the third metal layer M3 or even higher, as thedesign is required or preferred.

FIG. 6C shows deformation of the MEMS device 30 as the temperatureincreases. Compared with FIG. 6A, the thermal deformation of the MEMSdevice 30 is much more reduced and even better than the embodiment ofFIG. 6B.

Further, in the embodiment of FIG. 3, the feature that the recess isremoved and that the signal transmission structure 302 does not includethe first metal layer M1 can be implemented alone, independent of thedisconnected metal segments Mt1; that is, the top metal layer Mt of theMEMS structure 301 can be a continuous structure as shown in FIG. 1.

Referring to FIG. 4, according to another perspective, the presentinvention provides a MEMS device 40 with enhanced structural strength,which includes a MEMS structure 401, a signal transmission structure402, and a fixing member 403. The MEMS structure 401 includes pluralmetal layers M2-Mt, namely, from the second metal layer M2 to the topmetal layer Mt. The top metal layer Mt includes plural metal segmentsMt1 and the metal segments Mt1 are not directly connected with eachother; each of the metal segments Mt1 is individually connected to anadjacent metal layer Mt−1 (“adjacent metal layer” means a metal layerthat is immediately above or under; the metal layer Mt−1 is immediatelyunder the top metal layer Mt) through at least one supporting pillar,and there is no dielectric layer between the metal segments Mt1 and theadjacent metal layer Mt−1. The other metal layers (for example, from thesecond metal layers M2 to the metal layer Mt−1) are respectivelyconnected to their adjacent metal layers through at least one supportingpillar, and there can be a dielectric layer at least partially filling(shown as fully filling in the figure) between two adjacent metallayers.

In this embodiment, the fixing member 403 is located under and connectedto a bottom of the MEMS structure 401, not at a lateral side of the MEMSstructure 401, which is different from the embodiment shown in FIG. 2.From top view, the fixing member 403 is located inside the MEMSstructure 401. The fixing member 403 includes a portion (metal segmentM11) of the first metal layer M1, one or more dielectric layers, andsupporting pillars that connect the metal segment M11 to the MEMSstructure 401 and the substrate Sub. Note that the locations and numberof the supporting pillars show in the figure are for illustrativepurpose only and can be modified. There is similarly a recess 22 underthe MEMS structure 401 at the location above the signal transmissionstructure 402 to form a buffer space, and the recess 22 (or bufferspace) is farther from the center of the MEMS structure 401 than thefixing member 403 is (in the embodiment of FIG. 2, the recess 22 or thebuffer space is nearer to the center of the MEMS structure 201 than thefixing member 203 is).

FIG. 5 shows a MEMS device 50 according to another embodiment of thepresent invention. This embodiment is different from the embodiment ofFIG. 4 in that the MEMS device 50 includes plural metal segments M11 andthus plural fixing members 503 (two metal segments M11 and fixingmembers 503 as shown in the figure as a non-limiting example). Similarto the embodiment of FIG. 4, there is a recess 22 under the MEMSstructure 501 at the location above the signal transmission structure502 to form a buffer space. The recess 22 (or buffer space) is fartherfrom the center of the MEMS structure 201 than the fixing member 503 is.

FIGS. 6D and 6E show deformation of the MEMS device 40 of FIG. 4 anddeformation of the MEMS device 50 of FIG. 5 as the temperatureincreases, which show better performances of the MEMS devices 40 and 50than FIG. 6A and even better than FIG. 6B. That is, FIGS. 6D and 6Eillustrate that the MEMS devices 40 and 50 have more stable structuresand therefore a better performance in electric signal transmission.

In the embodiments of FIGS. 4 and 5, the lowest metal layer of the MEMSstructure is illustrated by the second metal layer M2 as an example;however, the lowest metal layer of the MEMS structure can be a highermetal layer such as the third metal layer M3 or even higher, as thedesign is required or preferred. In this case, the fixing members 403and 503 can correspondingly include a portion of the first metal layerM1, a portion of the second metal layer M2 (and a portion of one or moreeven higher metal layers as the case may require), dielectric layers,and supporting pillars connecting within the MEMS structures 401 and 501and connecting the MEMS structures 401 and 501 to the substrate Sub.

Further, in the embodiments of FIGS. 4 and 5, the feature that therecess 22 (or buffer space) is farther from the center of the MEMSstructure 503 than the fixing member 503 is can be implemented alone,independent of the disconnected metal segments Mt1; that is, the topmetal layer Mt of the MEMS structure 401 or 501 can be a continuousstructure as shown in FIG. 1.

FIG. 7 shows a MEMS device 70 according to another embodiment of thepresent invention. Different from FIG. 2, the signal transmissionstructure 202 of the MEMS device 70 is not adjacent to the fixing memberand has a considerable distance from the fixing member 203 (therefore,the fixing member is not shown in figure). For example, this distance dcan be larger than three times of the size of the fixing member in theshown direction. In this embodiment, the fixing member can be connectedto a lateral side of the MEMS structure 201 as shown in FIG. 2, orconnected to a bottom of the MEMS structure 201 as shown in FIGS. 4 and5.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the scope of the present invention. Those skilled in this artcan readily conceive variations and modifications within the spirit ofthe present invention. Therefore, all these and other modificationsshould fall within the scope of the present invention. An embodiment ora claim of the present invention does not need to attain or include allthe objectives, advantages or features described in the above. Theabstract and the title are provided for assisting searches and not to beread as limitations to the scope of the present invention.

What is claimed is:
 1. A MEMS device with enhanced structural strength,comprising: a MEMS structure, including a plurality of metal layerswhich include a top metal layer, the top metal layer including aplurality of metal segments which are not directly connected with oneanother; and a signal transmission structure under the MEMS structurefor transmitting an electric signal generated by the MEMS structure;wherein each of the metal segments is individually connected to anadjacent metal layer through at least one supporting pillar, and thereis no dielectric layer between the metal segments and the adjacent metallayer, and wherein except the top metal layer, the other metal layersare respectively connected to their adjacent metal layers through atleast one supporting pillar, with a dielectric layer at least partiallyfilling between two adjacent metal layers.
 2. The MEMS device withenhanced structural strength of claim 1, further comprising a fixingmember or a flexible member connected to the MEMS structure.
 3. The MEMSdevice with enhanced structural strength of claim 2, wherein the fixingmember is connected to a lateral side of the MEMS structure.
 4. The MEMSdevice with enhanced structural strength of claim 3, further comprising:a recess under the MEMS structure at a location above the signaltransmission structure.
 5. The MEMS device with enhanced structuralstrength of claim 3, wherein a lowest metal layer of the MEMS structureis continuous to the fixing member at the lateral side of the MEMSstructure and does not have a disconnection area above the signaltransmission structure.
 6. The MEMS device with enhanced structuralstrength of claim 5, wherein the signal transmission structure does notcomprise a metal layer as defined by CMOS manufacturing processterminology and the signal transmission structure includes a conductivewiring at a level below the metal layer.
 7. The MEMS device withenhanced structural strength of claim 2, wherein the fixing member isconnected to a bottom of the MEMS structure.
 8. The MEMS device withenhanced structural strength of claim 7, further comprising: a recessunder the MEMS structure at a location above the signal transmissionstructure, wherein the recess is farther from the center of the MEMSstructure than the fixing member is.